U.S. patent application number 14/890403 was filed with the patent office on 2016-04-28 for method and device for transmitting data in wireless communication system supporting dual connectivity.
This patent application is currently assigned to Pantech Inc.. The applicant listed for this patent is Pantech Inc.. Invention is credited to Jae Hyun AHN, Kang Suk HUH, Myung Cheul JUNG, Ki Bum KWON.
Application Number | 20160119826 14/890403 |
Document ID | / |
Family ID | 51867525 |
Filed Date | 2016-04-28 |
United States Patent
Application |
20160119826 |
Kind Code |
A1 |
HUH; Kang Suk ; et
al. |
April 28, 2016 |
METHOD AND DEVICE FOR TRANSMITTING DATA IN WIRELESS COMMUNICATION
SYSTEM SUPPORTING DUAL CONNECTIVITY
Abstract
Disclosed are a method and a device for transmitting data in a
wireless communication system supporting dual connectivity. The
method for transmitting data in a wireless communication system
supporting dual connectivity comprises the steps of: transmitting
channel state information between a small base station and a
terminal to a macro base station; receiving a radio resource
control (RRC) connection reconfiguration message from the macro
base station; releasing a connection with the small base station on
the basis of the RRC connection reconfiguration message; and
transmitting, to the macro base station, a PDCP state report
including information on a sequence number of a packet data
convergence protocol (PDCP) service data unit (SDU) which has not
been received.
Inventors: |
HUH; Kang Suk; (Seoul,
KR) ; KWON; Ki Bum; (Seoul, KR) ; AHN; Jae
Hyun; (Seoul, KR) ; JUNG; Myung Cheul; (Seoul,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Pantech Inc. |
Seoul |
|
KR |
|
|
Assignee: |
Pantech Inc.
Seoul
KR
|
Family ID: |
51867525 |
Appl. No.: |
14/890403 |
Filed: |
May 9, 2014 |
PCT Filed: |
May 9, 2014 |
PCT NO: |
PCT/KR2014/004185 |
371 Date: |
November 10, 2015 |
Current U.S.
Class: |
370/332 |
Current CPC
Class: |
H04W 76/15 20180201;
H04W 92/20 20130101; H04W 36/04 20130101; H04W 36/0044 20130101;
H04W 36/38 20130101 |
International
Class: |
H04W 36/00 20060101
H04W036/00; H04W 36/38 20060101 H04W036/38; H04W 36/04 20060101
H04W036/04 |
Foreign Application Data
Date |
Code |
Application Number |
May 10, 2013 |
KR |
10-2013-0053407 |
Claims
1. A method of receiving, by user equipment, data again in a
wireless communication system supporting dual connectivity, the
method comprising: receiving, from a small evolved-NodeB (eNB), a
part of packet data convergence protocol (PDCP) service data units
(SDUs); sending, to a macro eNB, information about a channel state
between the small eNB and the user equipment; receiving, from the
macro eNB, a radio resource control (RRC) connection
reconfiguration message; releasing connection with the small eNB
based on the RRC connection reconfiguration message; and sending,
to the macro eNB, a PDCP status report comprising information about
a sequence number of at least one PDCP SDU not received due to the
release of the connection with the small eNB.
2. The method of claim 1, wherein: the PDCP SDUs are received by
the macro eNB via an external packet data network, and the part of
the PDCP SDUs are transmitted to a radio link control (RLC) layer
of the small eNB.
3. The method of claim 1, wherein: the PDCP status report further
comprises at least one of PDCP status report generation cause
information and cell identifier information, the PDCP status report
generation cause information comprises information about a cause of
a generation of the PDCP status report, and the cell identifier
information comprises information about an identifier of a cell
which sends the PDCP status report.
4. The method of claim 3, further comprising receiving a
not-received PDCP SDU again from the macro eNB.
5. The method of claim 4, wherein the not-received at least one
PDCP SDU is retransmitted by the macro eNB based on the PDCP status
report.
6. The method of claim 3, wherein the part of the PDCP SDUs is
determined by the macro eNB based on the information about the
channel state.
7. A method of retransmitting, by a macro evolved-NodeB (eNB), data
in a wireless communication system supporting dual connectivity,
the method comprising: sending a part of packet data convergence
protocol (PDCP) service data units (SDUs) to a radio link control
(RLC) layer of a small eNB; receiving information about a channel
state between a user equipment and the small eNB from the user
equipment; determining whether to release a connection between the
user equipment and the small eNB based on the information about the
channel state; sending a radio resource control (RRC) connection
reconfiguration message to the user equipment if it is determined
that the connection between the user equipment and the small eNB is
released; and receiving, from the user equipment, a PDCP status
report comprising information about a sequence number of at least
one PDCP SDU not received by the user equipment.
8. The method of claim 7, further comprising a step of receiving
the PDCP SDUs received by a packet data convergence protocol (PDCP)
layer over an external the packet data network.
9. The method of claim 7, wherein: the PDCP status report further
comprises at least one of PDCP status report generation cause
information and cell identifier information, the PDCP status report
generation cause information comprises information about a cause of
a generation of the PDCP status report, and the cell identifier
information comprises information about an identifier of a cell
which sends the PDCP status report.
10. The method of claim 9, further comprising retransmitting at
least one PDCP SDU not received by the user equipment.
11. The method of claim 10, wherein the at least one PDCP SDU not
received by the user equipment is determined and the at least one
PDCP SDU is retransmitted based on the PDCP status report.
12. The method of claim 9, wherein the part of the PDCP SDUs is
determined based on the received channel state information.
13. A user equipment configured for receiving data again in a
wireless communication system supporting dual connectivity data,
the user equipment comprising: a receiver configured to receive a
part of packet data convergence protocol (PDCP) service data units
(SDU) from a small eNB; a processor configured to generate
information about a channel state between the small eNB and the
user equipment; a transmitter configured to send the information
about the channel state to a macro eNB, wherein the receiver is
configured to receive a radio resource control (RRC) connection
reconfiguration message from the macro eNB, the processor is
configured to release connection with the small eNB based on the
RRC connection reconfiguration message and generates a PDCP status
report comprising information about a sequence number of at least
one PDCP SDU which has not been received, the transmitter is
configured to send the PDCP status report to the macro eNB, the
PDCP SDUs are received by the macro eNB over an external packet
data network, and the part of the PDCP SDUs is received by the
reception unit through a radio link control (RLC) layer of the
small eNB.
14. The user equipment of claim 13, wherein: the PDCP SDUs are
received by the macro eNB over an external packet data network, and
the part of the PDCP SDUs is transmitted to a radio link control
(RLC) layer of the small eNB.
15. The user equipment of claim 13, wherein: the PDCP status report
further comprises at least one of PDCP status report generation
cause information and cell identifier information, the PDCP status
report generation cause information comprises information about a
cause of a generation of the PDCP status report, and the cell
identifier information comprises information about an identifier of
a cell which sends the PDCP status report.
16. The user equipment of claim 15, wherein the receiver receives
the not-received at least one PDCP SDU from the macro eNB.
17. The user equipment of claim 16, wherein the not-received at
least one PDCP SDU is retransmitted by the macro eNB based on the
PDCP status report.
18. The user equipment of claim 15, wherein the part of the PDCP
SDUs is determined by the macro eNB based on the information about
the channel state.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a National Stage Entry of International
Application PCT/KR2014/004185, filed on May 9, 2014, and claims
priority from and the benefit of Korean Patent Application No.
10-2013-0053407 filed on May 10, 2013, each of which is hereby
incorporated by reference for all purposes as if fully set forth
herein.
BACKGROUND
[0002] 1. Field
[0003] The present invention relates to wireless communications
and, more particularly, to a data transmission and device in a
wireless communication system supporting dual connectivity.
[0004] 2. Discussion of the Background
[0005] A cellular is a concept proposed to overcome a restriction
to a service area and the limits of the frequency and subscriber
capacities. A cellular is a method of providing coverage by
changing a single high-output base station to a plurality of
low-output base stations. That is, a mobile communication service
area is divided into several small cells, different frequencies are
allocated to neighboring cells, and the same frequency band is used
in two cells not having interference therebetween because they are
sufficiently spaced apart from each other, so the frequency is
spatially reused. Alternatively, a method of dividing a mobile
communication service area into several small cells, allocating the
same frequency to neighboring cells, but controlling the cells in
order to remove interference between the cells may also be
used.
[0006] Meanwhile, in a specific area, such as a hotspot within a
cell, many communication demands are specially generated. In a
specific area, such as a cell edge or a coverage hole, reception
sensitivity of radio waves may be deteriorated. As the wireless
communication technology is advanced, small cells, for example, a
pico cell, a femto cell, a micro cell, a remote radio head (RRH), a
relay, and a repeater are together installed within a macro cell in
order to enable communication in an area, such as a hotspot, a cell
edge, or a coverage hole. The small cells may be placed in the
outside or inside the macro cell. In this case, the small cell is
placed at the location where the macro cell is not reached, in the
inside of a house, or in an office. Such a network is called a
heterogeneous network (HetNet). In this case, the heterogeneous
network does not need to use a different radio access method. In a
heterogeneous network environment, a macro cell is a cell having
relatively large coverage, and a small cell, such as a femto cell
or a pico cell, is a cell having relatively small coverage. The
macro cell and the small cell may distribute the same traffic, or
each of which may be responsible for the transmission of traffic
having different QoS. In a heterogeneous network environment,
coverage overlap is generated between a plurality of macro cells
and small cells.
[0007] In a heterogeneous network environment, a dual connectivity
scheme has been introduced as one of cell planning schemes for
distributing an excessive load or a load required by specific QoS
to a small cell without a handover procedure and efficiently
sending data. From a viewpoint of a terminal, dual connectivity may
be a scheme for providing a more efficient method in terms of a
transmission/reception transfer rate. For example, a terminal may
send/receive services to/from two or more serving cells. In this
case, each of the serving cells may belong to a different base
station. In the area in which coverage of a macro cell overlaps
coverage of a small cell as described above, a terminal may
simultaneously connect (or signaling connection) to the macro cell
and the small cell or may simultaneously use (or user traffic
transmission) the macro cell and the small cell. This may be called
dual connectivity. That is, the terminal may be wirelessly
connected to two or more different base stations (e.g., a macro
base station including a macro cell and a small base station
including a small cell) through different frequency bands based on
the dual connectivity scheme and may send/receive services to/from
the two or more different base stations. Alternatively, the
terminal may be wirelessly connected to two or more different base
stations through the same frequency band and may send/receive
services to/from the two or more different base stations.
[0008] A terminal supporting dual connectivity can maintain two
radio links because it may simultaneously use a macro cell and a
small cell. If connection between a small base station and a
terminal is released while data is transmitted from a macro base
station and the small base station to the terminal based on dual
connectivity, an unnecessary reduction in transmission efficiency
of TCP packets may occur. There is a need for a method for
preventing such an unnecessary reduction in transmission efficiency
of TCP packets.
SUMMARY
[0009] An object of the present invention is to provide a method of
receiving data again in a wireless communication system supporting
dual connectivity.
[0010] Another object of the present invention is to provide a
method of retransmitting data in a wireless communication system
supporting dual connectivity.
[0011] Yet another object of the present invention is to provide a
device for performing a method of receiving data again in a
wireless communication system supporting dual connectivity.
[0012] Yet another object of the present invention is to provide a
device for performing a method of retransmitting data in a wireless
communication system supporting dual connectivity.
Technical Solution
[0013] In accordance with an aspect of the present invention, there
is provided a method of receiving, by user equipment, data again in
a wireless communication system supporting dual connectivity. The
method of receiving data again includes the steps of receiving a
part of packet data convergence protocol (PDCP) service data units
(SDU) from a small eNB, sending information about the channel state
between the small eNB and the user equipment to a macro eNB,
receiving a radio resource control (RRC) connection reconfiguration
message from the macro eNB, releasing connection with the small eNB
based on the RRC connection reconfiguration message, and sending a
PDCP status report including information about the sequence number
of at least one PDCP SDU not received due to the release of the
connection with the small eNB to the macro eNB.
[0014] In accordance with another aspect of the present invention,
there is provided a method of retransmitting, by a macro eNB, data
in a wireless communication system supporting dual connectivity.
The method of retransmitting data includes the steps of sending a
part of PDCP SDUs to the radio link control (RLC) layer of a small
eNB, receiving information about the channel state between user
equipment and the small eNB from the user equipment, determining
whether to release connection between the user equipment and the
small eNB based on the information about the channel state, sending
a radio resource control (RRC) connection reconfiguration message
to the user equipment if it is determined that the connection
between the user equipment and the small eNB is released, and
receiving a PDCP status report including information about the
sequence number of at least one PDCP SDU not received by the user
equipment from the user equipment.
[0015] In accordance with yet another aspect of the present
invention, there is provided user equipment receiving data again in
a wireless communication system supporting dual connectivity data.
The user equipment includes a reception unit receiving a part of
packet data convergence protocol (PDCP) service data units (SDU)
from a small eNB, a processor generating information about the
channel state between the small eNB and the user equipment, a
transmission unit sending the information about the channel state
to a macro eNB. The reception unit receives a radio resource
control (RRC) connection reconfiguration message from the macro
eNB. The processor releases connection with the small eNB based on
the RRC connection reconfiguration message and generates a PDCP
status report including information about the sequence number of at
least one PDCP SDU which has not been received. The transmission
unit sends the PDCP status report to the macro eNB. The PDCP SDUs
are received by the macro eNB over an external packet data network.
The part of the PDCP SDUs are received by the reception unit
through a radio link control (RLC) layer of the small eNB.
[0016] In accordance with the present invention, a reduction in the
transfer rate of a transmission control protocol (TCP) packet which
may unnecessarily occur if connection between UE and a small cell
is released while data is transmitted and received between a macro
cell and the UE and between the small cell and the UE based on dual
connectivity can be prevented.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 shows a wireless communication system to which the
present invention is applied.
[0018] FIG. 2 shows an example of the dual connectivity situation
of UE applied to the present invention.
[0019] FIG. 3 shows an example of a logical path setup for a macro
eNB and a small eNB in the dual connectivity situation of UE
according to an embodiment of the present invention.
[0020] FIG. 4 is a conceptual diagram showing the structure of dual
connectivity according to an embodiment of the present
invention.
[0021] FIG. 5 is a conceptual diagram showing a data transmission
and reception method if a small eNB is released while data is
transmitted based on dual connectivity according to an embodiment
of the present invention.
[0022] FIG. 6 is a conceptual diagram showing the information
format of a PDCP status report according to an embodiment of the
present invention.
[0023] FIG. 7 is a flowchart showing an operation of UE according
to an embodiment of the present invention.
[0024] FIG. 8 is a flowchart showing an operation of a macro eNB
according to an embodiment of the present invention.
[0025] FIG. 9 is a block diagram of UE, a macro eNB, and a small
eNB which perform radio link control in a wireless communication
system supporting dual connectivity according to the present
invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0026] Hereinafter, in this specification, some embodiments will be
described in detail with reference to exemplary drawings. It is to
be noted that in assigning reference numerals to elements in the
drawings, the same reference numerals denote the same elements
throughout the drawings even in cases where the elements are shown
in different drawings. Furthermore, in describing the embodiments
of this specification, a detailed description of the known
functions and constitutions will be omitted if it is deemed to make
the gist of the present invention unnecessarily vague.
[0027] Furthermore, in this specification, a wireless communication
network is described as a target, and tasks performed in the
wireless communication network may be performed in the process in
which a system (e.g., a base station) managing the corresponding
wireless communication network controls the network and sends data
or may be performed by a terminal which is combined with the
corresponding wireless communication network.
[0028] FIG. 1 shows a wireless communication system to which the
present invention is applied. The wireless communication system may
be the network structure of an evolved-universal mobile
telecommunications system (E-UMTS). The E-UMTS system may also be
called a long term evolution (LTE) or LTE-advanced (LTE-A) system.
The wireless communication systems are widely deployed in order to
provide various communication services, such as voice and packet
data.
[0029] Meanwhile, multiple access schemes applied to the wireless
communication system are not limited. Various multiple access
schemes, such as code division multiple access (CDMA), time
division multiple access (TDMA), frequency division multiple access
(FDMA), orthogonal frequency division multiple access (OFDMA),
single carrier-FDMA (SC-FDMA), OFDM-FDMA, OFDM-TDMA, and OFDM-CDMA,
may be used.
[0030] In this case, in uplink transmission and downlink
transmission, a time division duplex (TDD) method of performing
transmission using different times may be used, or a frequency
division duplex (FDD) method of performing transmission using
different frequencies may be used.
[0031] Referring to FIG. 1, an E-UTRAN includes a base station (BS)
20 which provides a control plane and a user plane to user
equipment (UE) 10. The user plane is a protocol stack for user data
transmission, and the control plane is a protocol stack for control
signal transmission. The UE 10 may be fixed or may have mobility
and may be called a different term, such as a mobile station (MS),
an advanced MS (AMS), a user terminal (UT), a subscriber station
(SS), or a wireless device.
[0032] The BS 20 commonly refers to a station communicating with
the UE 10 and may be called a different term, such as an
evolved-NodeB (eNB), a base transceiver system (BTS), an access
point, a femto-eNB, a pico-eNB, a home eNB, or a relay. The eNB 20
may provide at least one cell to UE. The cell may mean a
geographical area in which the eNB 20 provides communication
services or may mean a specific frequency band. The cell may mean
downlink frequency resources and uplink frequency resources.
Alternatively, the cell may mean a combination of downlink
frequency resources and optional uplink frequency resources.
[0033] The eNBs 20 may be connected through an X2 interface. The
eNB 20 is connected to an evolved packet core (EPC) 30 through an
S1 interface. More specifically, the eNB 20 is connected to a
mobility management entity (MME) through an S1-MME and to a serving
gateway (S-GW) through an S1-U. The S1 interface exchanges pieces
of operation and management (OAM) information for supporting the
mobility of the UE 10 by exchanging signals with the MME.
[0034] The EPC 30 includes the MME, the S-GW, and a packet data
network-gateway (P-GW). The MME includes access information about
the UE 10 or information about the capabilities of the UE 10. Such
information is chiefly used in the mobility management of the UE
10. The S-GW is a gateway having the E-UTRAN as an end point, and
the P-GW is a gateway having a packet data network (PDN) as an end
point.
[0035] The E-UTRAN and the EPC 30 may be integrated and called an
evolved packet system (EPS). A traffic flow up to a PDN for
connection from a radio link through which the UE 10 accesses the
eNB 20 to a service entity operates based on an Internet protocol
(IP).
[0036] A radio interface between UE and an eNB is called a Uu
interface. The layers of a radio interface protocol between the UE
and a network may be classified into L1 (a first layer), L2 (a
second layer), and L3 (a third layer) based on the lower three
layers of an open system interconnection (OSI) reference model
which has been widely known in communication systems. A physical
(PHY) layer belonging to the first layer of the lower three layers
provides information transfer services using physical channels. A
radio resource control (RRC) layer placed in the third layer
functions to control radio resources between the UE and the
network. To this end, in an RRC layer, RRC messages are exchanged
between the UE and the eNB.
[0037] The physical (PHY) layer provides information transfer
services to an upper layer using a physical channel. The PHY layer
is connected to a medium access control (MAC) layer (that is an
upper layer) through a transport channel. Data is moved between the
MAC layer and the PHY layer through the transport channel. The
transport channel is classified depending on how data is
transmitted through a radio interface according to what
characteristic. Furthermore, data is moved through a physical
channel between different PHY layers, that is, between the PHY
layers of a transmitter and a receiver. The physical channel may be
modulated according to an orthogonal frequency division
multiplexing (OFDM) method and uses time and a frequency as radio
resources. There are some physical control channels. A physical
downlink control channel (PDCCH) notifies UE of the resource
allocation of a paging channel (PCH) and a downlink shared channel
(DL-SCH) and hybrid automatic repeat request (HARM) information
related to the DL-SCH. The PDCCH may carry an uplink scheduling
grant which notifies UE of the resource allocation of uplink
transmission. A physical control format indicator channel (PCFICH)
notifies UE of the number of OFDM symbols used in PDCCHs and is
transmitted for each subframe. A physical hybrid ARQ indicator
channel (PHICH) carries HARQ ACK/NAK signals in response to uplink
transmission. A physical uplink control channel (PUCCH) carries
uplink control information, such as HARQ ACK/NAK, a scheduling
request, and CQI for downlink transmission. A physical uplink
shared channel (PUSCH) carries an uplink shared channel
(UL-SCH).
[0038] The functions of the MAC layer include mapping between a
logical channel and a transport channel and
multiplexing/demultiplexing in a transport block provided as a
physical channel on the transport channel of an MAC service data
unit (SDU) belonging to a logical channel. The MAC layer provides a
service to a radio link control (RLC) layer through a logical
channel. The logical channel may be divided into a control channel
for transferring control region information and a traffic channel
for transferring user domain information.
[0039] The functions of the RLC layer include the concatenation,
segmentation, and reassembly of an RLC SDU. In order to guarantee a
pieces of various quality of service (QoS) necessary for a radio
bearer (RB), the RLC layer provides three types of operation mode,
such as transparent mode (TM), unacknowledged mode (UM)m and
acknowledged mode (AM). AM RLC provides error correction through an
automatic repeat request (ARQ).
[0040] The functions of a packet data convergence protocol (PDCP)
layer in a user plane includes the transfer, header compression,
and ciphering of user data. The functions of a packet data
convergence protocol (PDCP) layer in a control plane include the
transfer and encryption/integrity protection of control plane
data.
[0041] The RRC layer is related to the configuration,
reconfiguration, and release of RBs and is responsible for control
of logical channels, transport channels, and physical channels. An
RB means a logical path provided by the first layer (PHY layer) and
the second layer (the MAC layer, the RLC layer, the PDCP layer) in
order to transfer data between UE and a network. The configuration
of an RB means the process of defining the characteristics of a
radio protocol layer and a channel in order to provide a specific
service and configuring each detailed parameter and operating
method. An RB may be divided into a signaling RB (SRB) and a data
RB (DRB). The SRB is used as a passage through which an RRC message
and an NAS message are transmitted in a control plane. The DRB is
used as a passage through which user data is transmitted in a user
plane.
[0042] A non-access stratum (NAS) layer placed higher than the RRC
layer performs functions, such as session management and mobility
management.
[0043] If RRC connection is present between the RRC layer of UE and
the RRC layer of an E-UTRAN, the UE is in RRC connected mode. If
not, the UE is in RRC idle mode.
[0044] In a heterogeneous network environment in which macro cells
and small cells are together deployed, the small cell is
advantageous compared to the macro cell in terms of the throughput
which may be provided to a single piece of UE because the small
cell provides services to an area smaller than the area of the
macro cell. However, UE once connected to a macro cell is unable to
receive a service from a small cell without performing handover
although it is placed in the service area of the small cell.
Furthermore, there are problems in that handover may be frequently
generated because the small cell has small coverage although the UE
is connected to the small cell through handover while moving and
this is not preferred in terms of network efficiency.
[0045] Accordingly, in a heterogeneous network environment, a dual
connectivity scheme has been introduced as one of cell planning
schemes for distributing an excessive load or a load required by
specific QoS to a small cell without a handover procedure and
efficiently transmitting data. From a viewpoint of UE, dual
connectivity may be a scheme for a more efficient method in terms
of a transmission/reception transfer rate. For example, UE may
send/receive services to/from two or more serving cells. In this
case, each of the serving cells may belong to a different eNB. The
UE may be wirelessly connected to two or more different eNBs (e.g.,
a macro eNB including a macro cell and a small eNB including a
small cell) through different frequency bands based on the dual
connectivity scheme and may send/receive services to/from the two
or more different eNBs. Alternatively, the UE may be wirelessly
connected to two or more different eNBs through the same frequency
band and may send/receive services to/from the two or more
different eNBs.
[0046] A dual connectivity situation is described below.
[0047] UE may receive services through different frequency bands
from a small eNB including only at least one small cell and a macro
eNB including only at least one macro cell. An eNB having low
transmission power, such as a small eNB, is also called a low power
node (LPN). RRC for maintaining connection mode with the UE may be
present in the macro eNB or the small eNB. In the following
contents, it is assumed that RRC for maintaining connection mode
with UE is present in a macro eNB.
[0048] FIG. 2 shows an example of the dual connectivity situation
of UE applied to the present invention.
[0049] Referring to FIG. 2, an F2 frequency band is allocated to a
macro eNB, and an F1 frequency band is allocated to a small eNB. UE
is in a situation in which the UE may send/receive a service
through the small cell using the F1 frequency band from the small
eNB while sending/receiving a service through the macro cell using
the F2 frequency band from the macro eNB. As described above, the
UE supporting dual connectivity may simultaneously use the macro
cell of the macro eNB and the small cell of the small eNB and
requires individual radio link control because radio links are
respectively configured between the UE and the macro eNB (or the
macro cell) and between the UE and the small eNB (or the small
cell).
[0050] FIG. 3 shows an example of a logical path setup for a macro
eNB and a small eNB in the dual connectivity situation of UE
according to an embodiment of the present invention.
[0051] Referring to FIG. 3, the macro eNB includes a PDCP entity,
an RLC entity, an MAC entity, and a PHY layer, but the small eNB
includes an RLC entity, an MAC entity, and a PHY layer. RBs are
respectively configured in the macro eNB and the small eNB with
respect to a single EPS bearer, and a service is provided to the
UE. That is, a service is provided to the UE through a flow#1
through the macro eNB and a flow#2 through the small eNB with
respect to a single EPS bearer.
[0052] The PDCP entity of the macro eNB is connected to the RLC
entity of the small eNB using an Xa interface protocol through a
backhaul. In this case, the Xa interface protocol may be an X2
interface protocol defined between eNBs within an LTE system.
[0053] The UE may send/receive data services through both the RB #1
of the macro eNB and the RB #2 of the small eNB with respect to an
EPS bearer.
[0054] FIG. 4 is a conceptual diagram showing the structure of dual
connectivity according to an embodiment of the present
invention.
[0055] Referring to FIG. 4, a single radio bearer corresponding to
a single EPS bearer may be separated from an RLC layer 420, that
is, a lower layer of the PDCP layer 410 of a macro eNB. A PDCP SDU
may be delivered to the RLC layer 420 of the macro eNB 403 and the
RLC layer 430 of a small eNB 406 on the basis of the PDCP layer 410
of the macro eNB. That is, packet data transmitted through an S-GW
400 may be distributed and delivered to the RLC layer 420 of the
macro eNB 403 and the RLC layer 430 of the small eNB 406. The PDCP
SDU may be distributed on the basis of the sequence number of the
PDCP SDU. For example, a PDCP SDU having a sequence number
corresponding to an add number may be transmitted to UE 450 through
the RLC layer 420 of the macro eNB 403. A PDCP SDU having a
sequence number corresponding to an even number may be transmitted
to the UE 450 through the RLC layer 420 of the small eNB 403. A
data multi-transmission method for a single service based on such a
dual connection method may be called a multi-flow method.
[0056] The UE 450 may receive data transmitted through the macro
eNB 403 and the small eNB 406. The data transmitted by the two eNBs
are merged in the PDCP layer 460 of the UE 450 and may be delivered
to the upper layer 470 of the UE 450.
[0057] Hereinafter, an embodiment of the present invention
discloses a data transmission and reception method between UE and a
macro eNB if connection between a small eNB and the UE is released
while data is transmitted from the macro eNB and the small eNB to
the UE based on dual connectivity. If connection between a small
eNB and UE is released while data is transmitted from a macro eNB
and the small eNB to the UE based on dual connectivity, an
unnecessary reduction in transmission efficiency of TCP packets may
occur. Hereinafter, an embodiment of the present invention
discloses a method of preventing an unnecessary reduction in
transmission efficiency of TCP packets.
[0058] FIG. 5 is a conceptual diagram showing a data transmission
and reception method if a small eNB is released while data is
transmitted based on dual connectivity according to an embodiment
of the present invention.
[0059] FIG. 5 discloses a connection configuration and a data
transmission and reception method between UE, a small eNB, a macro
eNB, and an S-GW.
[0060] RRC connection may be established between the macro eNB and
the UE (S500).
[0061] When the RRC connection is established between the macro eNB
and the UE, a configuration for the operation of a PDCP layer may
be performed. If a backhaul set up between the macro eNB and the
small eNB is a non-ideal backhaul, latency may be increased in
sending data from the small eNB to the UE. For example, latency if
a backhaul between the macro eNB and the small eNB is not ideal may
be increased to 60 ms. Accordingly, for data transmission and
reception between the eNB and the UE based on dual connectivity, a
reduction of the transfer rate needs to be prevented by separately
setting a PDCP discard timer with respect to a PDCP SDU transmitted
to the small eNB.
[0062] The PDCP discard timer may be a timer performing the
following operations.
[0063] The PDCP discard timer may be a timer for determining
whether to discard a PDCP SDU and/or a PDCP PDU in the PDCP layer
of a macro eNB. For example, the PDCP SDU may be received from the
upper layer (e.g., an Internet protocol (IP) of the PDCP layer of
the macro eNB. In this case, the PDCP discard timer may be started
in each PDCP SDU. If a condition in which the PDCP discard timer is
stopped is not present and when an operating PDCP discard timer
expires, the macro eNB may discard the PDCP SDU and the PDCP PDU.
Furthermore, when the PDCP discard timer expires, notification may
be provided to the RLC layer so that it discards an RLC SDU. The
RLC layer may discard the RLC SDU if any segment of the
corresponding RLC SDU has not yet been mapped to the RLC PDU after
notification is provided to the RLC layer so that it discards the
RLC SDU.
[0064] Furthermore, when an RRC connection procedure is performed,
the PDCP discard timer may determine whether UE will send PDCP
status information (PDCP status report) to a macro eNB. For
example, the value of an rlc-AM small cell release is true and
connection between a small eNB and UE is released, the UE may send
PDCP status information to the small eNB.
[0065] Table 1 below is an example of PDCP configuration
information transmitted through an RRC message when RRC connection
is established.
[0066] Table 1
TABLE-US-00001 TABLE 1 PDCF-Config ::= SEQUENCE { discardTimer for
macro cell ENUMERATED { ms50, ms100, ms150, ms300, ms500, ms750,
ms1500, infinity } OPTIONAL, --Cond Setup discardTimer for small
cell ENUMERATED { ms50, ms100, ms150, ms300, ms500, ms750, ms1500,
infinity } OPTIONAL, -- rlc-AM SEQUENCE { stausReportRequired
BOOLEAN } rlc small cell release SEQUENCE { statusReportRequired
BOOLEAN } OPTIONAL, --
[0067] If PDCP data is transmitted through the small eNB and the
macro eNB based on dual connectivity, the PDCP data may be
transmitted to the macro eNB through the S-GW over an external
packet data network. That is, the PDCP data may be transmitted from
the S-GW to the PDCP layer of the macro eNB through a single EPS
bearer. For example, it may be assumed that the sequence numbers of
PDCP SDUs transmitted to the PDCP layer of the macro eNB are 90,
91, 92, 93, 94, 95, 96, 97, 98, and 99. The plurality of PDCP SDUs
transmitted to the PDCP layer of the macro eNB may be divided and
transmitted to the macro eNB and the small eNB (S510).
[0068] The PDCP layer of the macro eNB may distribute the PDCP SDUs
to the respective eNBs based on the channel state between each eNB
(the macro eNB and the small eNB) and the UE, for example. For
example, the PDCP layer of the macro eNB may determine a ratio in
which an optimal transfer rate can be obtained based on the channel
state between the macro eNB and the UE and the channel state
between the small eNB and the UE and may distribute the PDCP SDUs
to the respective eNBs. The UE may measure a downlink channel state
based on a reference signal transmitted by each eNB. The UE may
feed the measured downlink channel state information back to each
eNB in a specific cycle or continuously. For example, the channel
state information between the small eNB and the UE may be fed back
to the macro eNB or the small eNB and the macro eNB at the same
time. For another example, after the channel state information
between the small eNB and the UE is first fed back to the small
eNB, the channel state information may be transmitted from the
small eNB to the macro eNB based on the interface between the small
eNB and the macro eNB.
[0069] The macro eNB may distribute the PDCP SDU to the RLC layer
of each eNB based on the received channel state information between
the small eNB and the UE and the received channel state information
between the macro eNB and the UE. That is, the macro eNB may
distribute and send the PDCP SDUs so that an eNB in a better
channel state has a higher data rate than an eNB in a relatively
poor channel state.
[0070] Hereinafter, in an embodiment of the present invention, for
convenience of description, it is assumed that a PDCP SDU having a
sequence number of an even number is distributed to the small eNB
and a PDCP SDU having a sequence number of an add number is
distributed to the macro eNB. That is, sequence numbers 90, 92, 94,
96, and 98 may be transmitted from the macro eNB to the small eNB
and may be transmitted from the small eNB to the UE again. Sequence
numbers 91, 93, 95, 97, and 99 may be transmitted from the macro
eNB to the UE.
[0071] The UE sends signal intensity information about the small
eNB to the macro eNB (S520).
[0072] The UE may send a measurement report to the macro eNB. The
measurement report may include signal intensity information between
the UE and the small eNB. For example, if the UE deviates from
coverage of the small eNB, signal intensity between the UE and the
small eNB may become weak. The UE may send the measurement report
to the macro eNB. The macro eNB may determine whether to release
the connection between the UE and the small eNB based on the
measurement report information.
[0073] The macro eNB sends an RRC connection reconfiguration
message to the UE (S530).
[0074] The macro eNB may determine to release the connection
between the small eNB and the UE. In this case, the macro eNB may
release the connection between the small eNB and the UE by sending
an RRC connection reconfiguration message to the UE. The UE may
receive the RRC connection reconfiguration message and perform RLC
re-establishment. When receiving the RRC connection reconfiguration
message from the macro eNB, the RLY layer of the UE may reassemble
RLC PDUs that have been successfully received with RLC SDUs and
sequentially deliver the combined results to the PDCP layer in
order of RLC sequence numbers. In contrast, the AM data (AMD) PDU
of an RLC layer that has been incompletely received is discarded.
In FIG. 5, it is assume that RLC SDUs corresponding to PDCP SDUs
corresponding to the sequence numbers 94 and 98 have been
incompletely received and discarded in the RLC layer.
[0075] The S-GW sends subsequent data to the macro eNB (S540).
[0076] The packet data network continues to send data to the PDCP
layer of the macro eNB. For example, PDCP SDUs corresponding to
sequence numbers 100, 101, 102, 103, and 104 may be transmitted
from the packet data network to the PDCP layer of the macro
eNB.
[0077] The macro eNB may send the PDCP SDUs transmitted by the
packet data network to the UE (S550).
[0078] For example, the macro eNB may send the PDCP SDUs
corresponding to the sequence numbers 100 and 101 to the UE.
[0079] The UE may send a PDCP status report to the macro eNB
(S560).
[0080] The PDCP status report may be used for the UE to receive a
PDCP SDU, not been received from a source cell, from a target cell
when the UE performs handover from the source cell to the target
cell. Furthermore, when connection between the small cell and the
UE is released, the PDCP status report may be used for the UE to
receive a PDCP SDU, not received from the small cell, from the
macro cell. That is, in dual connectivity between the UE and the
small cell and between the UE and the macro cell, when connection
between the small cell and the UE is released, the PDCP status
report may be used for the UE to receive a PDCP SDU, not received
from the small cell, from the macro cell. Furthermore, when the UE
moves to another small cell while maintaining dual connectivity
with another small cell in dual connectivity between the UE and the
small cell and between the UE and the macro cell, the PDCP status
report may be used for the UE to receive a PDCP SDU, not received
from a source small cell, from the macro cell or a target small
cell.
[0081] The PDCP status report may include information about PDCP
SDUs which have been received and not received by the UE.
Information about a PDCP SDU not received by the UE may be
transmitted to the macro eNB through a PDCP SDU that belongs to
PDCP SDUs that have not been received and that has the smallest
number and a bitmap generated based on the corresponding sequence
number. For example, if the UE has not received PDCU SDUs
corresponding to the sequence numbers 94 and 98, {94, 1, 1, 1, 0}
may be included in the PDCP status report and transmitted. The UE
may indicate a reception success (1) and non-reception (0) in the
value (first missing SN: FMS) of a non-reception PDCP sequence
number at the first (the smallest number) in the sequence of the
sequence numbers of the PDCP SDU and each SN after the FMS and may
send the PDCP status report to the PDCP layer of the eNB of the
macro cell. That is, {94, 1, 1, 1, 0} means {94(the smallest
sequence number), 1(95), 1(96), 1(97), 0(98)}.
[0082] If the UE has not sent a PDCP status report to the macro
eNB, a reduction of TCP performance may occur. In the PDCP layer of
the macro eNB, the PDCP discard timer of each of the PDCP SDUs 94
and 98 not received by the UE may be operating. The PDCP layer of
the macro eNB is unaware whether the UE has received a specific
PDCP SDU until the PDCP discard timer expires. Accordingly, the
macro eNB is unable to retransmit the PDCP SDUs, not received by
the UE, to the UE.
[0083] The UE may receive the PDCP SDUs from the macro eNB again
because the macro eNB may retransmit the PDCP SDUs if the macro eNB
has been aware that the UE had not received the PDCP SDUs. However,
since the macro eNB is unaware that the UE has not received the
PDCP SDUs, it does not retransmit the PDCP SDUs although it is able
to retransmit the PDCP SDUs. As a result, on the TCP transmission
side, the retransmission timers of a TCP packet related to the PDCP
SDUs not received by the UE expires. This is considered to be a
loss of the corresponding TCP packet, and thus the window size of
the TCP transmission side is reduced by half.
[0084] In this case, since the PDCP SDU buffer of the macro eNB is
almost full, the TCP transfer rate is inevitably lowered although
the PDCP SDUs may have been transmitted to the UE through the RLC
stage until the PDCP discard timers expire. The reason for this is
that a TCP transmission window size is reduced by half although it
is not necessary to reduce the TCP transmission window size by half
from a viewpoint of the TCP transmission side because the PDCP SDU
buffer is almost full. That is, there may be a problem in that the
TCP transfer rate is reduced although there is no problem
attributable to the PDCP SDU buffer in delivering the TCP packet to
the UE. Whenever a single TCP packet is considered to be a loss,
the TCP transmission window is reduced by half. Accordingly, for
example, if it is determined that three TCP packets have been
reduced within a short time, the transfer rate may also be reduced
to 1/8 because the TCP transmission window is reduced to 1/8. In
order to solve such a problem, an embodiment of the present
invention can prevent a problem in that the TCP transfer rate is
unnecessarily reduced as described above by notifying the macro eNB
of the sequence numbers of PDCP SDUs not received by the UE through
the PDCP status report.
[0085] Furthermore, in accordance with an embodiment of the present
invention, the PDCP status report may include information about a
cause of the generation of the PDCP status report. For example, a
cause of a cell release, that is, PDCP status report generation
cause information, may be included in the PDCP status report in the
form of a bit value, and transmitted. The PDCP status report
generation cause may be represented based in several indices. For
example, the index value 1 of the PDCP status report generation
cause may indicate that the PDCP status report has been generated
due to a cell release.
[0086] The macro eNB may be aware that a cause of the PDCP status
report is that the connection between the small cell and the UE has
been released on the basis of the PDCP status report generation
cause included in the received PDCP status report while performing
data transmission and reception based on dual connectivity. In this
case, the macro eNB may selectively retransmit only PDCP SDUs that
belong to PDCP SDUs included in the PDCP SDU buffer and that have
been delivered to the small eNB.
[0087] Furthermore, the PDCP status report may additionally include
cell information about whether the PDCP status report is a report
attributable to the RLS re-establishment of which cell. That is,
the PDCP status report may additionally include information about
the cell identifier of the small cell. For example, the cell
identifier information included in the PDCP status report may be a
physical cell identifier (PCI).
[0088] In the aforementioned embodiment of the present invention, a
method of preventing an unnecessary reduction of TCP performance
based on a PDCP status report has been disclosed, but performance
can be improved using the PDCP status report according to an
embodiment of the present invention even in the case of a user
datagram protocol (UDP) in addition to the TCP. That is, in the
case of the TCP, the transfer rate reduction problem can be solved
based on the PDCP status report transmitted by the UE. In the case
of the UDP, QoS of data can be improved by reducing a loss of data
of a real-time service (e.g., voice over LTE (VoLTE)) which is
sensitive to delay.
[0089] The macro eNB may send PDCP SDUs, not received by the UE, to
the UE (S570).
[0090] The macro eNB may be aware that the PDCP SDUs 94 and 98 that
the UE had tried to send have not been transmitted through the
small eNB based on the PDCP status information. The macro eNB may
first send the PDCP SDUs 94 and 98 (non-reception data), not
received by the UE, to the UE instead of the PDCP SNs 102, 103, . .
. , that is, the buffer ring sequence of the PDCP SDUs.
[0091] The macro eNB may send the buffered PDCP SDUs to the UE
(S580).
[0092] The macro eNB may send the PDCPs 102, 103, 104, . . . to the
UE in order in which the PDCPs 102, 103, 104, . . . have been
buffered in the PDCP SDU buffer.
[0093] FIG. 6 is a conceptual diagram showing the information
format of a PDCP status report according to an embodiment of the
present invention.
[0094] Referring to FIG. 6, the PDCP status report may include a
D/C 600, a PDU type 610, an FMS 620, a bitmap 630, PDCP status
report generation cause information 640, and cell identifier
information 650.
[0095] The D/C 600 may include information about whether a PDU is a
control PDU or a data PDU. For example, if the D/C 600 has a value
of 1, it may be aware that a PDU is a control PDU. If the D/C 600
has a value of 0, it may be aware that a PDU is a data PDU.
[0096] The PDU type 610 may indicate that a current PDU has what
type. For example, the PDU type 610 may indicate whether a current
PDU is a PDCP status report based on the PDU type 610.
[0097] The FMS 620 may include information about the sequence
number of a PDCP SDU that has not been first received by the UE as
described above.
[0098] The bitmap 630 may include information about other PDCP
SDUs, not received by the UE, in a bitmap based on the sequence
number of the PDCP SDU that has not been first received by the UE
as described above.
[0099] The PDCP status report generation cause information 640 may
include information about a cause of the generation of a PDCP
status report. The information about a cause of the generation of
the PDCP status report may be transmitted in the form of a bit
value based on a specific index. For example, if the PDCP status
report generation cause included in the PDCP status report is a
cell release between the small eNB and the UE, the information
about a cause of the generation of the PDCP status report may
correspond to an index 1. In this case, the PDCP status report
generation cause information 640 may include a bit value
corresponding to the index 1.
[0100] The PDCP status report may be generated for another cause.
In this case, the PDCP status report generation cause information
640 may send information about a cause of the generation of the
PDCP status report to the macro eNB based on a bit value.
[0101] The cell identifier information 650 may include information
about the identifier of a released small cell. The cell identifier
information may be the physical cell identifier (PCI) of a
cell.
[0102] Both the PDCP status report generation cause information 640
and the cell identifier information 650 may be included in the PDCP
status report, but only one of the PDCP status report generation
cause information 640 and the cell identifier information 650 may
be included in the PDCP status report. Hereinafter, for convenience
of description, it is assumed that both the PDCP status report
generation cause information 640 and the cell identifier
information 650 are included in the PDCP status report.
[0103] FIG. 7 is a flowchart showing an operation of UE according
to an embodiment of the present invention.
[0104] FIG. 7 discloses a method of sending, by UE, a PDCP status
report.
[0105] Referring to FIG. 7, the UE receives data from a macro eNB
and a small eNB based on dual connectivity (S700).
[0106] As described above, PDCP SDUs transmitted through the PDCP
layer of the macro eNB may be distributed to the RLC layers of the
macro eNB and the small eNB through a single EPS bearer. The
distributed PDCP SDUs may be transmitted to the UE through the
macro eNB and the small eNB.
[0107] The UE sends a measurement report to the macro eNB
(S710).
[0108] The UE may send downlink channel state information between
the small eNB and the UE to the macro eNB through the measurement
report.
[0109] The macro eNB may determine whether to release connection
between the small eNB and the UE based on the measurement report.
For example, if a downlink signal is a specific intensity or less,
the macro eNB may release connection between the small eNB and the
UE. For example, if the UE deviates from coverage of the small eNB,
the data transfer rate may be reduced because intensity of a signal
transmitted from the small eNB to the UE through a downlink channel
is reduced. In this case, the macro eNB may release connection
between the small eNB and the UE.
[0110] The UE receives an RRC connection reconfiguration message
transmitted by the macro eNB (S720).
[0111] If the channel state between the small eNB and the UE is not
good, the macro eNB may release connection between the small eNB
and the UE by sending an RRC connection reconfiguration
message.
[0112] The UE performs RLC re-establishment (S730).
[0113] The UE which has received the RRC connection reconfiguration
message may perform RLC re-establishment. The UE may sequentially
deliver RLC PDUs that have been successfully received to the PDCP
layer in order of the sequence numbers of the RLC PDUs based on the
RLC layer through the RLC re-establishment. When the RLC
re-establishment is performed, an RLC PDU that has been
incompletely received is discarded.
[0114] The UE generates a PDCP status report and sends it to the
macro eNB (S740).
[0115] The PDCP status report transmitted by the UE may include
information about PDCP SDUs that have not been received, PDCP
status report generation cause information, and cell identifier
information as in FIG. 6. When the UE sends the PDCP status report
information to the macro eNB, a performance reduction problem
generated because the connection between the UE and the small eNB
is broken and thus PDCP SDUs that need to be received by the UE
through the small eNB are not rapidly received can be solved.
[0116] The UE receives the PDCP SDUs that have not been received
(S750).
[0117] The macro eNB may retransmit the PDCP SDUs that have not
been received by the UE on the basis of the PDCP status report.
[0118] FIG. 8 is a flowchart showing an operation of a macro eNB
according to an embodiment of the present invention.
[0119] Referring to FIG. 8, the macro eNB determines whether to
release connection between a small eNB and UE based on a
measurement report transmitted by the UE (S800).
[0120] The measurement report may include channel state information
between the small eNB and the UE. For example, if intensity of a
signal transmitted from the small eNB to the UE is a specific
threshold or less, the macro eNB may determine whether to release
connection between the small eNB and the UE. This is one example in
which the macro eNB determines whether to release connection
between the small eNB and the UE. The macro eNB may determine
whether to release connection between the small eNB and the UE
using another method. For example, the macro eNB may determine
whether to release connection between the small eNB and the UE
based on another criterion other than the measurement report.
Hereinafter, it is assumed that the macro eNB determines to release
connection between the small eNB and the UE.
[0121] The macro eNB send an RRC connection reconfiguration message
to the UE (S810).
[0122] Connection between the UE and the small eNB may be released
based on the RRC connection reconfiguration message transmitted by
the macro eNB. The UE may perform RLC re-establishment after
receiving the RRC connection reconfiguration message.
[0123] The macro eNB receives a PDCP status report from the UE
(S820).
[0124] The macro eNB may obtain information about the sequence
numbers of PDCP SDUs not received by the UE, PDCP status report
generation cause information, and cell identifier information based
on the PDCP status report transmitted by the UE.
[0125] The macro eNB retransmits the PDCP SDUs, not received by the
UE, based on the received PDCP status report (S830).
[0126] The macro eNB may retransmit the PDCP SDUs not received by
the UE, based on the information about the sequence numbers of the
PDCP SDUs not received by the UE.
[0127] FIG. 9 is a block diagram of UE, a macro eNB, and a small
eNB which perform radio link control in a wireless communication
system supporting dual connectivity according to the present
invention.
[0128] Referring to FIG. 9, dual connectivity may be configured
between UE 900 according to the present invention and a macro eNB
930 and a small eNB 960. The UE 900 includes a UE reception unit
905, a UE transmission unit 910, and a UE processor 920. The UE
processor 920 performs required functions and control so that the
aforementioned characteristics of the present invention are
implemented.
[0129] The UE processor 920 may generate a measurement report based
on information about the channel state between the small eNB 960
and the UE 900. Furthermore, when connection between the small eNB
960 and the UE 900 is released, the UE processor 920 may generate a
PDCP status report.
[0130] The UE transmission unit 910 may send the measurement report
and the PDCP status report to the macro eNB 930.
[0131] The UE reception unit 905 may receive data transmitted by
the small eNB 960 and the macro eNB 930.
[0132] The macro eNB 930 includes a macro transmission unit 935, a
macro reception unit 940, and a macro processor 950.
[0133] The macro reception unit 940 may receive the measurement
report and the PDCP status report transmitted by the UE.
[0134] The macro processor 950 may determine whether to release
connection between the small eNB and the UE based on the
measurement report transmitted by the UE 900. Furthermore, the
macro processor 950 may determine whether to retransmit PDCP SDUs
not received by the UE 900 based on the received PDCP status
report.
[0135] The macro transmission unit 935 may retransmit the PDCP SDUs
not received by the UE 900.
[0136] Furthermore, the small eNB 960 includes a small reception
unit 965, a small transmission unit 970, and a small processor
980.
[0137] The small reception unit 965 may receive data transmitted by
the macro eNB 930. Furthermore, the small reception unit 965 may be
connected to the UE 900 and may send and receive data.
[0138] The small processor 980 may determine a data rate at which
data will be transmitted to the UE 900 based on the channel state
information transmitted by transmitted by the UE.
[0139] While some exemplary embodiments of the present invention
have been described with reference to the accompanying drawings,
those skilled in the art may change and modify the present
invention in various ways without departing from the essential
characteristic of the present invention. Accordingly, the disclosed
embodiments should not be construed as limiting the technical
spirit of the present invention, but should be construed as
illustrating the technical spirit of the present invention. The
scope of the technical spirit of the present invention is not
restricted by the embodiments, and the scope of the present
invention should be interpreted based on the following appended
claims. Accordingly, the present invention should be construed as
covering all modifications or variations derived from the meaning
and scope of the appended claims and their equivalents.
* * * * *